1. Field of the Invention
The present invention relates to industrial lift trucks such as forklift trucks, and more particularly concerns an improved device for indicating the tilt position of the mast which supports forwardly directed lifting forks.
2. Description of the Prior Art
Industrial forklift trucks are generally comprised of a wheeled chassis having a compartment which accommodates operating controls and a seated operator, and power means for moving the truck. Mounted to the forward end of the chassis is an upwardly directed mast which is pivotable with respect to the chassis. Tilting of the mast within a vertical plane is generally controlled by a tilt cylinder. A pair of forwardly directed forks are mounted for vertical sliding movement along the mast. As is known in the art, the forks may be inserted within a pallet which supports a load.
In most operations of a forklift, it is desirable that the forks be maintained in a horizontally level orientation. For example, a warehouse facility may typically provide for multiple pallets to be stacked on top of each other, wherein the pallet located on the uppermost level can be fifteen to twenty feet above the floor. Without maintaining the pallet at level or near level conditions, there is a danger of the pallet dropping with the possible injury to the workmen, the product, the pallet, or the forklift itself. Additionally, without maintaining the pallets in a level orientation, the pallets may not properly fit on top of the previous stack, resulting in the possibility of capsizing the stack.
In some operations, particularly when the forklift truck is riding upon an inclined surface, it may be necessary to adjust the angular position of the mast so as to bring the forks into a more horizontal disposition. In operations where the forks are at a very high elevation, it may be necessary to adjust the angle of the mast so as to maintain the center of gravity of the loaded truck within safe limits. Excessive incline of the mast can also cause damage to the outermost planks of a pallet.
In view of these concerns, various level indicating devices have been developed for forklifts, including those set forth in U.S. Pat. No. 3,312,361 to Foster; U.S. Pat. No. 3,865,265 to Brudi et. al. and U.S. Pat. No. 3,883,021 to Wilhelm. These devices essentially work on a plumb bob principle which indicates the degree of tilt of the mast assembly. The difficulty with such devices is that malfunctions of the plumb bob, caused by foreign matter or physical damage, are not easily detected. Lateral movement of the mast transversely to the vertical plane can also produce inaccurate results.
U.S. Pat. No. 5,697,755 to McCauley et. al. discloses a mechanical forklift level indicator which includes a first arm pivotably connected to the body of the forklift, and a second arm pivotably connected to the forklift mast assembly. Interaction of the arms with the mast indicate the relative orientation of the forks.
U.S. Pat. No. 5,749,696 to Johnson discloses a tilt sensor for the mast of a forklift truck. The sensor is incorporated into a tilt cylinder interactive between the mast and the, truck body. The sensor employs a magnet adapted to slide along a series of transistors, thereby producing electronic signals. The signals are routed to a computer controller which interacts electronically with a display unit providing illuminated position information to the operator.
The aforesaid earlier mast tilt indicator devices are generally of complex construction susceptible to breakage or malfunction under severe operating conditions, or in harsh environments. Also, the indicator mechanism is often not easily readable by the operator, thereby detracting from his full attention to the operation of the forklift truck. Some of the aforesaid devices may be suitably installed at the factory where the forklift truck is manufactured, but cannot readily be added onto an already manufactured forklift truck.
It is accordingly an object of the present invention to overcome the aforementioned drawbacks of the prior art by providing a simple, reliable device easily installable onto the mast of a forklift truck for indicating the angular position of the mast within a vertical plane.
A further object of this invention is to provide a mast position indicating device which can be easily viewed from the forklift operator's position.
It is still another object of the present invention to provide a durable mast position indicating device amenable to low cost manufacture.
These objects and other objects and advantages of the invention will be apparent from the following description.